In the field of information recording on a recording medium and information reproduction from a recording medium on which the information is recorded, under the circumstances wherein recording and reproduction of data representing moving pictures performed with a relatively small-scale recording and reproducing instrument are desired, it is strongly required more than before to have arrangements for recording information on a recording medium with high data density, increasing data rate of information to be recorded on or reproduced from a recording medium and so on. Accordingly, with the intention of meeting such requirements, there has been proposed an optical recording and reproducing technology for causing a single or a plurality of light beams to be incident upon an optical recording medium on which information can be recorded with light so as to record information on the optical recording medium and to reproduce information from the optical recording medium on which the information is recorded.
With the optical recording and reproducing technology, in addition to the advantage that noncontact information recording wherein information is subjected to noncontact recording on an optical recording medium or noncontact information reproduction wherein information recorded on an optical recording medium is subjected to noncontact reproduction from the optical recording medium is carried out, further advantages that a laser light beam is used for recording information on an optical recording medium so that the information is recorded with high data density on the optical recording medium and a plurality of independent laser light beams are used for recording information on and reproducing the information from an optical recording medium so that the data rate of the information to be recorded on or reproduced from the optical recording medium is increased, are obtained. As one of information recording and reproducing apparatus, to each of which such optical recording and reproducing technology as mentioned above is applied, an optical tape recording and reproducing apparatus in which a tape-shaped optical recording medium, namely, an optical tape is used, has been proposed as disclosed in the paper of “Novel digital optical tape recorder”, Oakley, William S., LaserTape Inc., SPIE Proceedings Vol. 2604, pp. 256–262.
FIG. 1 shows a light beam controlling and signal processing portion of an example of the optical tape recording and reproducing apparatus proposed previously. In the light beam controlling and signal processing portion shown in FIG. 1, a laser light source 1 is provided for generating continuously a single laser light beam as a parallel light beam. The single laser light beam emitted from the laser light source 1 enters into a beam producing hologram 2.
In the beam producing hologram 2, the single laser light beam which is the parallel light beam emitted from the laser light source 1 is divided into a plurality of laser light beams each being a parallel light beam. That is, the beam producing hologram 2 is operative to produce a plurality of parallel light beams by dividing the single parallel light beam.
The laser light beams obtained from the beam producing hologram 2 enter into a polarized light beam splitter 3 and are reflected from the polarized light beam splitter 3 to be directed downward in FIG. 1 to pass through a quarter wavelength plate 4 and then enter into a converging lens 5. The converging lens 5 is operative to converge the laser light beams having passed through the quarter wavelength plate 4 on a two-dimensional light-modulator 6.
The two-dimensional light-modulator 6 is constituted with a plurality of reflection type light-modulating elements which are arranged two-dimensionally with predetermined spaces. The laser light beams converged by the converging lens 5 come respectively to the reflection type light-modulating elements so arranged two-dimensionally as to form the two-dimensional light-modulator 6. A back surface of each of the reflection type light-modulating elements, which is opposite to an incident surface of the reflection type light-modulator upon which one of the laser light beams is incident, forms a light reflector. Therefore, the laser light beam incident upon each of the reflection type light-modulating elements is reflected from the light reflector in the form of the back surface of the reflection type light-modulator.
In relation to the two-dimensional light-modulator 6, a modulation control signal generator 7 is provided. The modulation control signal generator 7 is operative to produce a plurality of modulation control signals SM corresponding to information which are to be recorded and supply the reflection type light-modulating elements constituting the two-dimensional light-modulator 6 with the modulation control signals SM, respectively. Each of the reflection type light-modulating elements constituting the two-dimensional light-modulator 6 is operative to modulate the laser light beam which is incident thereupon and reflected therefrom in response to the modulation control signal SM. The modulation of the laser light beam in the two-dimensional light-modulator 6 is carried out by varying the reflection amount of the laser light beam at each of the reflection type light-modulating elements in response to the modulation control signal SM. Incidentally, if the modulation control signals SM require, the laser light beam which is incident upon each of the reflection type light-modulating elements constituting the two-dimensional light-modulator 6 is reflected from the reflection type light-modulating elements substantially without being modulated.
As a result of this, the laser light beams which are modulated in response to the modulation control signals SM at and reflected from the reflection type light-modulating elements arranged two-dimensionally with predetermined spaces, respectively, or reflected respectively from the reflection type light-modulating elements arranged two-dimensionally with predetermined spaces substantially without being modulated, are obtained from the two-dimensional light-modulator 6 to be directed to the converging lens 5.
The laser light beams from the two-dimensional light-modulator 6 pass through the converging lens 5 and the quarter wavelength plate 4 to enter into the polarized light beam splitter 3. Since the laser light beams entering into the polarized light beam splitter 3 from the quarter wavelength plate 4 have passed through the quarter wavelength plate 4 twice in the direction to the converging lens 5 and in the opposite direction to the polarized light beam splitter 3, a plane of polarization of each of the laser light beams entering into the polarized light beam splitter 3 from the quarter wavelength plate 4 has been rotated by 90 degrees in comparison with that of each of the laser light beams entering into the polarized light beam splitter 3 from the beam producing hologram 2 and therefore the laser light beams entering into the polarized light beam splitter 3 from the quarter wavelength plate 4 pass through the polarized light beam splitter 3 without being reflected.
The laser light beams thus having passed through the polarized light beam splitter 3 further pass through a quarter wavelength plate 8 and a light beam control optical system 9 to be incident upon an optical tape 10 which is an optical recording medium. The light beam control optical system 9 is operative to subject each of the laser light beams passing through there to the optical tape 10 to focus control for focusing properly each of the laser light beams on the optical tape 10 and tracking control for causing each of the laser light beams to be incident upon a proper position on the optical tape 10. Further, the optical tape 10 is driven by an optical tape driving device not shown in FIG. 1 to run in the direction indicated with an allow T (hereinafter, referred as the T direction).
With the movement of the optical tape 10 in the T direction, a plurality of recording tracks, on each of which information is recorded, are formed on the optical tape 10 along the moving direction of the optical tape 10.
When the laser light beams which have been reflected without being modulated from the two-dimensional light-modulator 6 are incident upon the optical tape 10, these laser light beams are modulated in response to information recorded on the optical tape 10 and simultaneously reflected from the optical tape 10 to be directed to the light beam control optical system 9. The laser light beams obtained from the optical tape 10 pass through the light beam control optical system 9 and the quarter wavelength plate 8 and then enter into the polarized light beam splitter 3. Since the laser light beams entering into the polarized light beam splitter 3 from the quarter wavelength plate 8 have passed through the quarter wavelength plate 8 twice in the direction to the light beam control optical system 9 and in the opposite direction to the polarized light beam splitter 3, a plane of polarization of each of the laser light beams entering into the polarized light beam splitter 3 from the quarter wavelength plate 8 has been rotated by 90 degrees in comparison with that of each of the laser light beams entering into the polarized light beam splitter 3 from the quarter wavelength plate 4 and therefore the laser light beams entering into the polarized light beam splitter 3 from the quarter wavelength plate 8 are reflected from the polarized light beam splitter 3 to be directed to the right in FIG. 1.
The laser light beams reflected to the right in FIG. 1 from the polarized light beam splitter 3 enter into a light beam splitter 11. A part of each of the laser light beams having entered into the light beam splitter 11 is reflected from the light beam splitter 11 to be directed downward in FIG. 1 to pass through an optical element 12, such as a cylindrical lens or the like, and then enters into a focus and tracking detector 13 and another part of each of the laser light beams having entered into the light beam splitter 11 passes through the light beam splitter 11 further to pass through an optical element 14, such as a converging lens or the like, and then enters into a light detector 15.
The focus and tracking detector 13 is operative to produce output signals SF and ST which represent respectively the focus condition and the tracking condition of the laser light beams incident upon the optical tape 10 in response to the laser light beams incident upon the focus and tracking detector 13 through the optical element 12. The output signals SF and ST thus obtained from the focus and tracking detector 13 are used for focus control and tracking control to which each of the laser light beams to be incident upon the optical tape 10 is subjected in the light beam control optical system 9.
The light detector 15 is operative to produce a plurality of output signals SI which vary in response to variations in each of the laser light beams incident upon the light detector 15 through the optical element 14 and supply an information reproducing portion 16 with the output signals SI. The information reproducing portion 16 is operative to reproduce the information recorded on the optical tape 10 based on the output signals SI obtained from the light detector 15.
In the optical tape recording and reproducing apparatus thus shown in FIG. 1, when information is newly recorded on the optical tape 10, the modulation control signals SM which are produced to vary in response to the information to be recorded are supplied from the modulation control signal generator 7 to the reflection type light-modulating elements constituting the two-dimensional light-modulator 6, respectively. As the result, the laser light beams which are modulated in response to the modulation control signals SM by the reflection type light-modulating elements and simultaneously reflected from the reflection type light-modulating elements are obtained from the two-dimensional light-modulator 6 to be directed to the converging lens 5.
The laser light beams modulated in response to the modulation control signals SM and obtained from the two-dimensional light-modulator 6 pass through the converging lens 5, the quarter wavelength plate 4, the polarized light beam splitter 3 and the quarter wavelength plate 8 to enter into the light beam control optical system 9 and then are subjected to the focus control and the tracking control in the light beam control optical system 9 so as to be incident upon the optical tape 10. As a result of this, the recording of the information on the optical tape 10 is carried out with the laser light beams modulated in response to the modulation control signals SM and the recording tracks, on each of which the information is recorded, are formed on the optical tape 10.
When information recorded on the optical tape 10 is reproduced from the optical tape 10 in the optical tape recording and reproducing apparatus shown in FIG. 1, the modulation control signals SM, each of which is predetermined to be constant, are supplied from the modulation control signal generator 7 to the reflection type light-modulating elements constituting the two-dimensional light-modulator 6, respectively. As the result, the laser light beams which are reflected with a constant reflecting amount without being modulated from the reflection type light-modulating elements are obtained from the two-dimensional light-modulator 6 to be directed to the converging lens 5.
The laser light beams having not been modulated and obtained from the two-dimensional light-modulator 6 pass through the converging lens 5, the quarter wavelength plate 4, the polarized light beam splitter 3 and the quarter wavelength plate 8 to enter into the light beam control optical system 9 and then are subjected to the focus control and the tracking control in the light beam control optical system 9 so as to be incident upon the optical tape 10. The laser light beams thus incident upon the optical tape 10 are modulated in response to the information recorded on the optical tape 10 and simultaneously reflected from the optical tape 10 to be directed to the light beam control optical system 9. The laser light beams modulated in response to the information recorded on the optical tape 10 and obtained from the optical tape 10 pass through the light beam control optical system 9 and the quarter wavelength plate 8 and then are reflected from the polarized light beam splitter 3 to enter into the light beam splitter 11. The laser light beams thus entering into the light beam splitter 11 are partially reflected from the light beam splitter 11 to enter into the focus and tracking detector 13 and simultaneously partially pass through the light beam splitter 11 to enter into the light detector 15 through the optical element 14.
As a result of this, the output signal SF which represents the focus condition of the laser light beams incident upon the optical tape 10 and the output signal ST which represents the tracking condition of the laser light beams incident upon the optical tape 10 are obtained from the focus and tracking detector 13 and the output signals SI which vary in response to variations in each of the laser light beams modulated in response to the information recorded on the optical tape 10 are obtained from the light detector 15 to be supplied to the information reproducing portion 16. Then, in the information reproducing portion 16, the information recorded on the optical tape 10 is reproduced based on the output signals SI obtained from the light detector 15.
The optical tape 10 on which the information is recorded or from which the information recorded thereon is reproduced in the optical tape recording and reproducing apparatus shown in FIG. 1, is driven to run by the optical tape driving device.
FIG. 2 shows an example of the optical tape driving device. In the optical tape driving device shown in FIG. 2, a supply reel 21 on which the optical tape 10 is wound to be derived therefrom and a take-up reel 22 onto which the optical tape 10 is wound are provided. The optical tape 10 between the supply reel 21 and the take-up reel 22 is driven by a friction capstan 23 to run in the T direction from the supply reel 21 to the take-up reel 22.
Further, in the optical tape driving device shown in FIG. 2, a plurality of positioning members 24, a pair of tension regulators 25 and a running guide member 26 are provided for causing the optical tape 10 driven by the friction capstan 23 to run stably though a predetermined position. The positioning members 24 determine a running path for the optical tape 10 and tension regulators 25 are operative to provide the optical tape 10 between the supply reel 21 and the take-up reel 22 with predetermined tensile force brought about by springs 27. The running guide member 26 serves for guiding the optical tape 10 so that the laser light beams obtained from a light beam controlling and signal processing portion 28, such as shown in FIG. 1, are incident upon the optical tape 10 on the running guide member 26.
As shown in FIG. 3, the running guide member 26 has a guide face portion 29 facing to the optical tape 10 and a flange portion 30 for restricting the position of the optical tape 10 running thought the guide face portion 29. The guide face portion 29 is formed into a partial cylindrical surface as shown in FIG. 4.
The main function required to be performed by the running guide member 26 in the optical tape driving device mentioned above is to maintain a space between the optical tape 10 and the guide face portion 29 to be extremely small, for example, 10 to 100 nm (nanometer) for stabilizing the position of the optical tape 10 running through the guide face portion 29 so that the incident position on the optical tape 10 of each of the laser light beams obtained from the light beam controlling and signal processing portion 28 is fixed invariably.
However, with the running guide member 26 in the optical tape driving device mentioned above, the optical tape 10 comes into concentrative contact with a portion of the guide face portion 29 which is very narrow in the T direction and extends along the width of the optical tape 10 because the guide face portion 29 is formed into the cylindrical surface as shown in FIG. 4 and therefore the space between the optical tape 10 and the guide face portion 29 which is required to be extremely small, for example, 10 to 100 nm, is formed only on the very narrow portion of the guide face portion 29. This means that an area on the guide face portion 29 where the incident position on the optical tape 10 of each of the laser light beams which are obtained from the light beam controlling and signal processing portion 28 is fixed invariably is limited to be very narrow. Further, the portion of the guide face portion 29 with which the optical tape 10 comes into concentrative contact is subjected to abrasion to be deformed and thereby it is feared that a disadvantage wherein the space between the optical tape 10 and the guide face portion 29 required to be extremely small, for example, 10 to 100 nm, is varied is brought about.
Accordingly, it is an object of the invention disclosed in each of claims of the present application to provide an apparatus for driving a tape-shaped optical recording medium which is provided with running guide means having a guide face portion for facing to a tape-shaped optical recording medium and capable of maintaining continuously a space between the tape-shaped optical recording medium and the guide face portion to be extremely small over a relatively wide area on the guide face portion and thereby is able to maintain stably an area on the guide face portion where the incident position on the tape-shaped optical recording medium of each of laser light beams obtained from a light beam controlling and signal processing portion is fixed invariably to be relatively wide.